The disclosure relates to an apparatus set up to carry out such a method, to a corresponding computer program and to a machine-readable storage medium having such a program.
A symmetrical cryptosystem is a cryptosystem in which, in contrast to an asymmetrical cryptosystem, both subscribers use the same key. The use of the same key for encryption and decryption entails the key itself first of all having to be transmitted before any encrypted interchange. However, since the security of the entire method depends on keeping the key secret, conventional approaches usually provide for the key to be interchanged via a secure channel.
In contrast, the practice of interchanging the key via non-secure channels is still a challenge for a person skilled in the art. In this respect, the prior art provides approaches such as the known Diffie-Hellmann key interchange or so-called hybrid encryption methods which make it possible to interchange symmetrical keys by incorporating asymmetrical protocols.
However, in the recent past, cryptosystems which move the problem of key interchange from the application layer of the OSI reference model to its physical layer (PHY) have been increasingly discussed.
Such approaches are used, for instance, in the still new field of cyber-physical systems which are distinguished by a high degree of complexity and the primary use of wireless and therefore inherently non-secure communication channels. Corresponding methods provide for each of the parties involved to derive a key from the technical properties of the channel connecting them in such a manner that the keys generated in this way largely match without the need to transmit specific parts of the key.
These cryptosystems therefore have the common feature of the need to eradicate discrepancies between the keys generated on both sides using the non-secure channel without weakening the negotiated key in the event of electronic eavesdropping. In order to solve this problem, U.S. Pat. No. 7,942,324 B1, for instance, proposes the use of the CASCADE protocol known from quantum computing.